
#include <cassert>
#include <cmath>
#include <iostream>
using namespace std;

int main() {
  int n = 12;
  double x1 = 20.0;
  double x2 = -10.0;
  double dx = (x1 - x2) / n;
  x1 += 2 * dx;
  x2 -= 2 * dx;

  int n1 = floor((x1 - x2) / dx);
  cout << n1 << endl;
  return 0;
}